Angiogenesis is the formation of new blood vessels from pre-existing vessels. Angiogenesis is prominent in solid tumor formation and metastasis. A tumor requires formation of a network of blood vessels to sustain the nutrient and oxygen supply for continued growth. Some tumors in which angiogenesis is important include most solid tumors and benign tumors, such as acoustic neuroma, neurofibroma, trachoma, and pyogenic granulomas. Prevention of angiogenesis could halt the growth of these tumors and the resultant damage due to the presence of the tumor.
It has been shown that there is a direct correlation between tumor microvessel density and the incidence of metastasis. Tumor cells themselves can produce factors that stimulate the proliferation of endothelial cells and new capillary growth. Angiogenesis is important in two stages of tumor metastasis. The first stage where angiogenesis stimulation is important is in the vascularization of the tumor, which allows tumor cells to enter the blood stream and to circulate throughout the body. After the tumor cells have left the primary site, and have settled into the secondary, metastasis site, angiogenesis must occur before the new tumor can grow and expand. Therefore, prevention of angiogenesis could lead to the prevention of metastasis of tumors and possibly contain the neoplastic growth at the primary site. These observations have led to the investigation of anti-angiogenic agents as possible therapeutic options for various cancers.
In the 1950's, thalidomide was marketed as a sedative in Europe but was withdrawn from the market when it was found to be a potent teratogen. Recently, thalidomide has been promoted as a possible inhibitor of angiogenesis. Studies have indicated, however, that thalidomide itself is not sufficiently active to inhibit angiogenesis. Instead, the anti-angiogenic activity or effects previously attributed to thalidomide are the resulting effects of compounds that are only present following metabolic activation of thalidomide (i.e., “active” thalidomide metabolites). D'Amato, R.; Loughman Flynn, E.; Folkman, J., Thalidomide as an Inhibitor of Angiogenesis. Proc. Nat'l. Acad. Sci., 1994, 91, 4082-4085; M.; Bauer, K.; Dixon, S.; Figg, W. Inhibition of Angiogenesis by Thalidomide Requires Metabolic Activation, Which Is Species-dependent. Biochem. Pharmacology, 1998, 55, 1827-1834. Accordingly, it has been speculated that certain metabolites of thalidomide rather than thalidomide itself are responsible for its anti-angiogenic properties. However, the specific thalidomide metabolites responsible for the anti-angiogenic properties have not yet been isolated and identified.
There are hundreds, if not thousands of compounds formed as a result of metabolism of thalidomide and the actively metabolized products of hydrolysis compounds of the thalidomide. Many of the thalidomide metabolites are inactive and/or unstable. There is no way to predict which metabolite(s) will have superior anti-angiogenic properties. As such, “active” thalidomide metabolites (or “active” thalidomide analogs) having superior anti-angiogenic properties are not yet available.
If the anti-angiogenic activity can be attributed to one or a small number of thalidomide metabolites and those metabolites could be isolated and identified, then active thalidomide analogs may be synthesized to provide exceptionally effective compounds inhibiting angiogenic effects. This is especially true when comparing thalidomide to “active” thalidomide analogs. To obtain such active compounds from thalidomide, thalidomide must first be activated via metabolism; only a very small amount of thalidomide would actually be metabolized to one or more “active” metabolites. Further, it may be possible to administer such “active” thalidomide analogs in lower amounts and still achieve the desired anti-angiogenic effects. Moreover, such “active” thalidomide analogs could be safer than thalidomide in avoiding undesirable side effects, e.g., teratogenicity or neurotoxicity, and may be more specific to tumor angiogenesis than thalidomide-thalidomide has a host of undesirable biological activities.
Accordingly, there is a need for isolation and identification of the thalidomide metabolites having superior anti-angiogenic properties. Further, there is a need for the synthesis of purified thalidomide analogs that can mimic the effects of the isolated and identified thalidomide metabolites that display such anti-angiogenic activity. In addition, there is a need for a method for treating undesired angiogenesis using such active thalidomide analogs.